The Interchange
High-speed road interchanges have been around for the best part of a century now even though viaducts that allow roads to cross without intersecting have a much longer history. Intersections have been around for as long as there have been roads but the problem with intersections is that give way rules such as “Give way to the right!” have to agreed upon and consistently observed. If they’re not, then alternating right of way can be regulated by traffic lights. Roundabouts solve the problem by making all traffic flow in the same direction before vehicles can exit, and so have the advantage of increasing the predictability of vehicle movement as long as the two rules of “Vehicles not on the roundabout must give way to vehicles on the roundabout” and “Vehicles on the roundabout must give way to vehicles exiting the roundabout” are followed. With higher traffic volumes, the first rule is usually regulated by the addition of traffic signals to control entry to the roundabout but, once a vehicle is in the roundabout, the driver must still be in the correct lane in order to safely exit. On the left below is Clocktower Roundabout, the first roundabout in Dubai, circa. 1963. On the right is Satwa Roundabout that was constructed about the same time but the image is from 2020 well after entry had been regulated by traffic signals.
The evolution of interchanges can be traced fairly easily in Dubai. The image on the left below is Trade Centre Roundabout in 1978, It’s a roundabout but with dual carriageways, perhaps in anticipation of more traffic but more likely because most roads in the UAE are dual carriageways anyway. The image one the right is Interchange 3, from the same year. You can see the evolution of right turn dedicated lanes to reduce the number of vehicles on the actual roundabout.
The following two images are Dubai’s Interchange #3 in 2007 and 2020 respectively. Apart from the road widening, the main 2007 improvement was to route the major artery beneath the roundabout to separate it from the minor route. It’s what’s known as a two-level interchange. Between 2007 and 2020, new entrance and exit ramps were added asymmetrically as needed. It’s not uncommon for interchanges to grow incrementally and in response to conditions that show at different stages over time and this is why most are asymmetrical.
Interchanges that are symmetrical along two axes are more likely to be on flat ground and with intersecting roads of equal importance. Another type of two-level interchange is what’s called the cloverleaf interchange. These use slip roads to handle all changes of direction, including U-turns. Their main disadvantage is that they require much land. Cloverleaf interchanges are gradually being phased out because of the two safety issues of 1) speeds on the curves being restricted and 2) necessary weaving of traffic entering and leaving the main roads. It was first patented in Maryland (US) by Arthur Hale in 1916.1
Stack interchanges don’t have this problem. Their major advantage is that they use less land. The history of interchanges must include the Four Level Interchange (a.k.a. the Four Level, or Stack)2 that opened in 1953. At the time, this particular interchange was seen as a symbol of modernity and, for decades after, aerial footage of it was to feature as three- or four-second opening credits scenes establishing LA as a location. [Photos: Caltrans]
Over the years, other types of intersections have been devised. I’ve already mentioned cloverleaf and stack. On the right below is a diagram showing the principle of the Pinavia interchange which is a variation of the Turbine or Windmill interchange. Each possible traffic destination has its own lane and this eliminates weaving and merging within the interchange itself. Pinavia interchanges are essentially two-level interchanges but, for reasons of space and construction expedience, ramps can be stacked. They are only two level which is good, but this comes at the cost of three additional bridges. Traffic throughput however, is 30% better than a stacked interchange.3 The owner of the US patent No. US-2007-0258759-A1 is S. Buteliauskas of the Military Academy of Lithuania.4
“Traffic goes in a circular motion, and no lanes need to be changed while passing the junction. The radii of all curves in the junction can be set equal or larger
than the smallest radius of the curves of the intersecting roads, so the driving speed in the junction can be equal to the speed on the intersecting roads. Rare in interchange design, it is possible to access and use the central area if a suitable use can be found.”5
This website covers some of the lesser-known variants.6 There are of course, composites and hybrids. Cloverleafs are still common. Here are some along the UAE’s Emirates Road.
This next one is the Huangjuewan Junction on the edge of the city of Chongqing in China. There is some disagreement about how many expressways and ramps it actually has. Some say three expressways and 28 ramps but Wikipedia says five expressways and 14 ramps7. Either way, there’s probably some reason why they all had to meet in a mountain valley. It’s probably the most complex interchange in the world but the complexity is magnified by the topographical restrictions. I only mention this as an example of an interchange which is not just about rerouting traffic.
Different things happen when there is the time and place to create or completely rebuild an interchange. This is another Emirates Road interchange, this time the one close to Miracle Gardens. The first image I saw was the one at left produced, it seems, by generative AI which isn’t so good at physical realities. It’s worrying that no editor at this publication called Construction Week noticed that the top level not only doesn’t work, but isn’t needed anyway in a cloverleaf intersection.
Here’s a clearer image that does nothing to explain why a roundabout has to be put above a cloverleaf interchange
It doesn’t really matter because it was only content. Below is the final interchange as built, and without the inner cloverleaf. You can have a look for yourself. It’s right next to Dubai Miracle Garden. It seems that two levels are all you need to create an ideal interchange, or a maximum of three if you’re stuck for space.
This is a conclusion of sorts to the brief history and evolution of the interchange but lastly, I have these two examples of interchanges along the Desheng Expressway in Hangzhou, China. Hangzhou is the city I’ve previously written about8 as having a mindset that everything must be beautiful. I was immediately struck by the rotational symmetry of these interchanges and how the ramps weren’t as stacked as they could have been if the main driver was to save space rather than keep the height low. I see this as a typical Hangzhou planning decision.
Apart from that 1953 interchange, there’s been very little aesthetic enthusiasm for interchanges. They remain stubbornly huge, visible, and concrete. The spaces between the ramps can’t be used for anything without compromising traffic and/or pedestrian safety. There is little option but to add landscaping but not to the degree that it becomes a distraction. Around 2013 the land under and around Dubai’s Interchange #3 was planted in a geometric pattern of grass and flowers to make it look more attractive in general, but particularly so when seen from Burj Khalifa and other surrounding tall buildings.
Surface level planting remains the first choice, with greening interchanges with a combination of creepers and vines being a second choice. Hangzhou does both.
A third option I see being explored more these days is decorative illumination but again, this can’t be so decorative as to be distracting. Here’s some images of Hanzhou interchanges9 with illumination that is about more than road safety.
- https://www-sop.inria.fr/galaad/conf/AuronSlides/Krasauskas.pdf ↩︎
- https://www.theguardian.com/cities/2015/apr/13/los-angeles-four-level-interchange-history-cities-50-buildings ↩︎
- https://www.academia.edu/26495834/Comparison_of_Pinavia_Interchange_Vs_Interchanges_All_Directional_and_Nano_of_Traffic_Operation_and_Safety_with_Traffic_simulation ↩︎
- https://www-sop.inria.fr/galaad/conf/AuronSlides/Krasauskas.pdf ↩︎
- https://www-sop.inria.fr/galaad/conf/AuronSlides/Krasauskas.pdf ↩︎
- https://www.sehinc.com/insights/amazing-world-interchange-designs ↩︎
- https://en.wikipedia.org/wiki/Huangjuewan_interchange ↩︎
- https://misfitsarchitecture.com/2026/05/10/misfits-guide-to-hangzhou-杭州）/ ↩︎
- https://www.chinadaily.com.cn/travel/2016-08/31/content_26653772.htm ↩︎
• • •
• • •
“The 2’nd Misfits’ Trienniale: WEEK 3”
“Architecture Misfit #33: Josef Frank”
“Dubai Deconstruction Update”
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